Transportable package with a cold box, and method for producing a low-temperature air separation system

ABSTRACT

The invention relates to a transportable package with a cold box, in the interior of which at least one double column of a low-temperature air separation system is arranged, i.e., a double column having a high-pressure column and a low-pressure column. The high-pressure and low-pressure columns contain mass transferring elements. The mass transferring elements in at least one sub-region of the low-pressure columns are formed by an ordered packing made of folded metal sheets having a thickness of 0.2 mm or less. The ordered packing has a specified surface area of at least 1000 m2/m3. At least in a sub-region of the high-pressure column, the mass transferring elements are formed by rectifying plates arranged one over the other and which have a clearance of less than 195 mm. The invention further relates to a method for producing a low-temperature air separation system using such a transportable package.

The invention relates to a transportable package with a cold box for a low-temperature air separation system according to the preamble of claim 1.

Such units are generally termed “packaged unit” (PU) and are described, for example, in EP 1041353 B1 or US 2007199344 A1.

Methods and devices for low-temperature separation of air are known in general, for example, from Hausen/Linde, Tieftemperaturtechnik [Low-temperature technology], 2^(nd) edition 1985, chapter 4 (pages 281 to 337).

The distillation column system can be constructed in the invention as a two-column system, in particular as a classical Linde double column system, or else as a three- or more column system. It can, in addition to the columns for nitrogen-oxygen separation, have further devices for producing high-purity products and/or other air components, in particular noble gases, for example an argon production with crude argon column and optionally with crude argon column and/or a krypton-xenon production.

Usually, in air separation systems, conventional rectification plates, for example bubble-cap plates or sieve plates, or ordered packings of a specific surface area (packing density) of 250 to a maximum of 750 m²/m³ are used. Hereinafter, the expressions “specific surface area of a packing” and “packing density” are used synonymously. A particularly “dense” packing therefore has a particularly high specific surface area.

A “cold box” here is taken to mean an insulating encasement which completely encases with outer walls a heat-insulated inner space; in the inner space, the system parts that are to be insulated are arranged, for example one or more separation columns and/or heat exchangers. The insulating action can be effected by corresponding configuration of the outer walls and/or by filling the intermediate space between system parts and outer walls with an insulating material. In the case of the latter variant, preferably a pulverulent material, such as, for example pearlite, is used. Not only the distillation column system for nitrogen-oxygen separation of a low-temperature air separation system but also the main heat exchanger and further cold system parts must be enclosed by one or more cold boxes. The external dimensions of the cold box usually determine the transport dimensions of the package in the case of prefabricated systems. The “height” of a cold box is taken to mean the dimension in the vertical direction based on the orientation of the cold box in system operation; the “cross section” is the surface perpendicular thereto (horizontal). During transport, the height of the cold box determines the transport length, the cross section transport height and cross section transport width.

PUs are fabricated in a factory, which are generally far removed from the installation site of the air separation system. This permits a substantial prefabrication and thereby minimization of the production expenditure at the installation site, where frequently very many difficult conditions prevail. The prefabricated package or a plurality of prefabricated packages are transported from the factory to the installation site, the cold box package with one or more separation columns in a horizontal arrangement. For such transports, restrictions with respect to the length and width of the packages exist. This technology is used to date only in air separation systems of medium size when the columns are at least in part equipped with ordered packings, because packed columns generally require a greater height than plate columns; the HETP value (HETP=height equivalent to a theoretical plate) of a 750-type packing is considerably greater than that of a sieve plate. Larger systems with packed columns are produced with a relatively low degree of prefabrication; in particular, the cold box is not constructed until at the installation site. Alternatively, exclusively conventional rectification plates are used; although this permits a relatively high capacity per unit height of the columns, it gives rise to traceably increased energy consumption compared with packing columns.

The object of the invention is to design a transportable package of the type mentioned at the outset in such a manner that it is also applicable to low-temperature air separation systems of a capacity for which to date prefabrication of the columns-cold box as a whole was not possible, wherein a more efficient energy consumption of the system should be achieved.

This object is achieved by the characterizing features of the patent claim.

Although it has already been proposed to use ordered packings of a packing density 750 m²/m³ and more, in order to decrease the height of the column (see for example EP 636237 B1=WO 9319336 A1=U.S. Pat. No. 5,613,374), such packings being regularly made of aluminum, in the case of PUs, use has to date not been made of such a dense packing, because with the dense packing at the same time an increase in the cross section of the column and thereby the transport width of the package beyond the permissible values would be associated therewith.

In the context of the invention, it has now turned out that, by using a packing of a particularly low sheet thickness, despite a high packing density, a surprisingly high value can be achieved for the capacity based on the cross section of the column; vice versa, this means a relatively low diameter of the columns for a particularly low height. In addition, in the invention, a particularly low height of the high-pressure column is achieved by installing rectification plates there, in particular sieve plates, more precisely having a particularly low plate spacing of less than 125 mm (the plate spacing is measured from the top side of a plate to the top side of the adjacent plate). For example, in the context of the invention, in the low-pressure column, exclusively ordered packing having a density of at least 1000 m²/m³ is used, and the high-pressure column contains exclusively sieve plates which overall have a lower plate spacing than 125 mm.

Relating to the cold box package, in the case of the invention, not only transport width but also transport height have relatively low values, despite high capacity of column and air separation system. The advantage of being able to prefabricate even air separation systems having a relatively high capacity in the form of a package of the type mentioned at the outset is so large that the increased costs are readily justified by using a special packing and a particularly low plate spacing.

In the invention, it can be expedient if, for example, at least one section of the low-pressure column is completely filled with the packing type described in patent claim 1. However, the invention can also be implemented as a result of the fact that the subregion, in which this specific packing is used, extends only over a part of a section of the low-pressure column, and in the remainder of this section, other mass transfer elements are installed.

In the invention, high-pressure column and low-pressure column are arranged in the form of a double column one above the other, wherein the double column is arranged in the interior of the cold box. Between high-pressure column and low-pressure column or in the sump of the low-pressure column, preferably a main condenser is situated which is constructed as a condenser-evaporator, and via which the two columns are in heat-exchanging connection. The expressions “top”, “bottom”, “above” and “below” here refer to the arrangement of the cold box in the installed ready-to-operate state.

With respect to the number of columns in the package, the invention can be employed in various variants, for example in the following:

The package contains only the double column and no further separation column.

The package, in addition to the double column, contains a crude argon column, which is arranged next to the low-pressure column, and optionally a pure argon column.

The package, in addition to the double column, contains a mixed column in which liquid oxygen product of the low-pressure column is vaporized in direct mass transfer with a part of the feed air, and finally produced as gaseous impure oxygen product, and which is arranged next to the low-pressure column.

The package, in addition to the double column, contains a medium-pressure column (flash column) in which crude oxygen from the high-pressure column is subjected to a further nitrogen-oxygen separation, and which is arranged next to the low-pressure column.

In the context of the invention, in particular a high-pressure column, a main condenser and a low-pressure column are arranged one above the other in a manner of a classical Linde double column.

If a crude argon column is used, this can be of a one-part type, as shown in EP 377117 B2=U.S. Pat. No. 5,019,145, or of a multi-part type, for example two-part, as shown in EP 628777 B1=U.S. Pat. No. 5,426,946.

Preferably, the plate spacing of the distillation plates in the high-pressure column is between 80 and 155 mm, in particular between 95 and 130 mm.

In the cold box, in addition, a crude argon column can be arranged. In another application, the cold box, in addition to the double column, does not contain a further separation column.

It is particularly expedient if the height of the cold box is less than 47 meters. A transport length of the package of less than 47.5 m may be achieved thereby.

Depending on transport conditions, in the context of the invention, a maximum cold box height of 40 to 43 meters can also be achieved. In a particularly preferred embodiment, the height of the cold box is between 29 and 47 meters, in particular between 35 and 43 meters. In this case, the cold box can also contain a separator (phase separator) for liquid nitrogen from the main condenser which is arranged at the top of the low-pressure column or thereabove.

Preferably, the “minimum diameter” of the cross section of the cold box is not more than 4.25 meters, and is preferably less than 4.15 meters. A transport height of the package of less than 4.30, or less than 4.20 meters, respectively, may be achieved thereby.

The “minimum diameter of the cross section of the cold box” is taken to mean the linear extent which determines the smaller of the two transport dimensions transversely to the direction of travel, customarily the transport height. This minimum diameter is, for example, in the case of a rectangular cross section, formed by the smaller side length, in the case of a square cross section, by the side length of the square, and in the case of a circular cross section by the diameter of the circle. In a particularly preferred embodiment, this “minimum diameter” is between 2.5 and 5 meters, in particular between 3 and 4.2 meters.

The diameter of the cross section of the cold box perpendicular thereto is preferably smaller than 5.95 meters, in particular less than 4.95 meters. This value determines the larger of the two transport dimensions transverse to the direction of travel, customarily the transport width. It allows thereby a transport width of less than 6.0 meters, or less than 5.0 meters, respectively, to be achieved. The said diameter dimension is, for example, between 2.0 and 6.0 meters, in particular between 3.0 and 5.0 meters.

It can be advantageous if, in the cold box (or in a further cold box, the argon box), in addition, a crude argon column is arranged in the cold box, which crude argon column has a top condenser which is constructed as condenser-evaporator, wherein the evaporation space of the top condenser is connected via a two-phase pipe to the low-pressure column, and the two-phase pipe is constructed in such a manner that, in operation of the low-temperature air separation system, not only gas but also liquid flow from the evaporation space of the top condenser at the same feed point into the low-pressure column. In this case, height for otherwise necessary distributors and collectors in the low-pressure column is saved. To minimize the height in packing columns, the gas and the liquid are fed from the argon system to the same point. Compared with a separate feed at different points, a distributor is saved, which demands about one meter in height. In the case of a particularly critical transport length, this variant can offer advantages, although it is less expedient in processing terms. In the cold box which contains the crude argon column, a pure argon column can be additionally arranged.

“Condenser-evaporator” designates a heat exchanger in which a first condensing fluid stream comes into indirect heat exchange with a second vaporizing fluid stream. Each condenser-evaporator has a liquefaction space and a vaporization space which consist of liquefaction passages and vaporization passages, respectively. In the liquefaction space, the condensation (liquefaction) of a first fluid stream is carried out, and in the vaporization space the vaporization of a second fluid stream is carried out. Vaporization and liquefaction spaces are formed by groups of passages which are in a heat-exchange relationship with one another.

In particular, when in the sump of the separation column, a condenser-evaporator is arranged (such as, for example, the main condenser in the sump of a low-pressure column), the metal sheets of the ordered packing which have a sheet thickness of 0.2 mm or less, consist of copper, more precisely, preferably immediately above the condenser-evaporator. Most preferably, they have a sheet thickness of 0.1 mm or less. For example, the mass transfer section immediately above the condenser-evaporator seen from the bottom, first has five layers of copper packing with more than 1000 m²/m³, and thereabove 15 layers of aluminum packing with more than 1000 m²/m³.

Owing to the mechanical material properties of copper, a very dense packing with very low sheet thickness can be produced without fabrication and quality problems occurring, as can occur in the case of aluminum sheets of low thickness.

“Copper” is here taken to mean pure copper or an alloy having a copper content of at least 67%, preferably at least 80%, most preferably at least 90% mass fraction. In particular, the expression “copper” comprises all materials named in annex C of the EIGA document IGC Doc 13/02/E as “copper” and “copper-nickel alloys” (“Copper”/“Copper-Nickel Alloys” in EIGA—OXYGEN PIPELINE SYSTEMS—IGC Doc 13/02/E published by European Industrial Gases Association).

Preferably, the ordered packing made of copper has a specific surface area of greater than 1000 m²/m³, in particular greater than 1150 m²/m³. For example, the packing density thereof can be 1200 or 1250 m²/m³.

Employing the invention is particularly expedient when the low-temperature air separation system is designed for processing more than 10 000 Nm³/h and less than 250 000 Nm³/h of feed air in standard operations.

The invention furthermore relates to a method for producing a low-temperature air separation system according to patent claim 10, in which the above described transportable package is used and, after transport to the installation site, is connected to an air compressor for compressing feed air, to a purification unit for compressed feed air, and to a main heat exchanger for cooling purified feed air. The purification unit is constructed, for example, as a molecular sieve adsorber. Alternatively, the air can also be purified in a reversible heat exchanger (Revex or regenerator); in this case, purification unit and main heat exchanger are formed from the same apparatus.

In a similar manner, the invention and the embodiments thereof can also be employed to somewhat larger systems, in which the transportable package only contains the separation column, that is to say for example the low-pressure column, the high-pressure column or the crude argon column of a low-temperature air separation system, or else a double column of high-pressure column, low-pressure column and main condenser arranged therebetween. In this case, the internally completely prefabricated column is transported to the construction site horizontally as a substantially cylindrical component and there provided with the insulated casing (cold box).

The invention and also further details of the invention will be described in more detail hereinafter with reference to an exemplary embodiment shown schematically in the drawings. In the drawings:

FIG. 1 shows a simplified process diagram of a low-temperature air separation system according to the invention,

FIG. 2 shows a simplified side view of a package according to the invention and

FIG. 3 shows the same package in plan view.

In the method shown in FIG. 1, purified air 1 is cooled in a main heat exchanger 2 against product streams to about dew point at a pressure of 4 to 20 bar, preferably 5 to 12 bar, and introduced into the distillation column system, which here has a high-pressure column 3, a low-pressure column 5 and a crude argon column 15. The high-pressure column 3 is in a heat-exchange relationship to a low-pressure column 5 via a shared condenser-evaporator 4, the main condenser. In the exemplary embodiment, all of the feed air 1 is introduced into the high-pressure column 3.

Sump liquid 6 and nitrogen 7 are taken off from the high-pressure column 3, subcooled in a counter flow heat exchanger 8 and throttled into the low-pressure column 5. From the low-pressure column, oxygen is withdrawn via product conduits oxygen 9, nitrogen 10 and impure nitrogen 11. The products can also be withdrawn at least in part in the liquid state. This is not shown in the method diagram for the sake of clarity.

Via an argon transfer conduit 14, an argon-containing oxygen stream is withdrawn from the lower region of the low-pressure column 5 (below the sump liquid conduit 6), passed into the lower region of a crude argon column 15 and there separated into a crude argon product 16 and a residual fraction 17. The residual fraction is passed back into the low-pressure column. It can either flow back (if a corresponding gradient is present) via the conduit 14 or, as shown in FIG. 1, be transported via a separate conduit 17 by means of a pump 18.

The top of the crude argon column is cooled by a crude argon condenser 19, on the vaporization side of which sump liquid introduced via conduit 20 from the high-pressure column 3 is vaporized. The vaporized fraction is conducted via conduit 21 to the low-pressure column. It can be introduced, for example, at the height of the sump liquid conduit 6. However, feed in between opening of the sump liquid conduit 6 and connection of the argon transfer conduit 14 is particularly advantageous.

In a known manner, in the method, cold is generated by work-producing expansion of one or more process streams in one or more turbines. This is not shown in the simplified diagram.

The low-pressure column 5, in the exemplary embodiment, has the following sections which are formed by in each case a packing section of ordered packing:

A pure nitrogen section (above the impure nitrogen conduit 11)

B Impure nitrogen section (restricted by impure nitrogen conduit 11 and sump liquid conduit 6)

C impure oxygen section (restricted by sump liquid conduit 6 and conduit 21 for introducing the partially vaporized fraction from the crude argon condenser 19)—in deviation from the depiction in the drawing, the packing of this section can utilize the entire region of the narrower diameter,

D argon intermediate section (restricted by conduit 21 for introducing the vaporized fraction from the crude argon condenser 19 and withdrawal conduit 14 for the argon-containing oxygen fraction to be separated in the crude argon column),

E oxygen section (below the withdrawal conduit 14 for the argon-containing oxygen fraction to be separated in the crude argon column and immediately above the sump evaporator=main condenser 4).

In the exemplary embodiment, the following mass transfer elements are used in the various sections of the low-pressure column 5:

A pure nitrogen section: ordered aluminum packing which consists of folded metal sheets of a sheet thickness of 0.10 mm and has a specific surface area of greater than 1000 m²/m³, in particular 1250 m²/m³

B impure nitrogen section: ordered aluminum packing which consists of folded metal sheets of a sheet thickness of 0.10 mm and has a specific surface area of 750 m²/m³

C impure oxygen section: ordered aluminum packing which consists of folded metal sheets of a sheet thickness of 0.10 mm and has a specific surface area of 750 m²/m³

D argon intermediate section: ordered aluminum packing which consists of folded metal sheets of a sheet thickness of 0.10 mm and has a specific surface area of greater than 1000 m²/m³, in particular 1250 m²/m³

E oxygen section: at least in the lowest part an ordered copper packing which consists of folded metal sheets of Cu-DHP R200 as specified in DIN EN 13599 of a sheet thickness of 0.05 mm and has a specific surface area of greater than 1000 m²/m³, in particular 1250 m²/m³. An aluminum packing as in section D follows thereabove.

The crude argon column 15 has five mass transfer sections. These are all formed in the exemplary embodiment by ordered packing which consists of folded aluminum sheets of a sheet thickness of 0.10 mm and has a specific surface area of greater than 1000 m²/m³, in particular 1250 m²/m³.

The high-pressure column 3 contains exclusively sieve plates. The plate spacing in the example is a constant 123 mm.

In a departure from the exemplary embodiment, within one or more of the above listed sections of the low-pressure column, combinations of different types of mass transfer elements can also be used, for example a combination of ordered packings of different specific surface area or different sheet materials or a combination of ordered packing and conventional rectification plates.

In a departure from the embodiment shown in FIG. 1, some of the air that is to be separated is work-producingly expanded in a turbine and, bypassing the preliminary separation in the high-pressure column 3, is injected directly into the low-pressure column 5, for example between sections C and D, or between sections B and C. In further differing embodiments, the crude argon column can be omitted and/or a mixed column supplemented, in which liquid oxygen product of the low-pressure column is vaporized in direct mass transfer with some of the feed air and finally produced as gaseous impure oxygen product.

In a further alternative embodiment, in at least one subregion of the crude argon column 15, an ordered packing is used which is formed from folded copper sheets and has a specific surface area of greater than 750 m²/m³, in particular greater than 1000 m²/m³, or greater than 1150 m²/m³, for example 1250, wherein the copper sheets have a sheet thickness of 0.1 mm or less, for example 0.05 mm.

In FIGS. 2 and 3, the corresponding parts of the device are designated with the same reference signs as in FIG. 1.

The transportable package which is part of a system according to FIG. 1, is encased by a cold box 51 which has the shape of a cuboid. Walls and roof of the cold box 51 are formed by steel support structures which are clad with metal sheets. The interior of the cold box is filled between system parts and the outer walls with a pulverulent insulating material such as, for example, pearlite.

The cold box 51 contains the double column of low-pressure column 5, high-pressure column 3 and the main condenser 4, and also the associated conduits, valves and metering devices. It is completely prefabricated as a package and is then transported to the installation site.

In FIG. 2, in addition, a separator (phase separator) for liquid nitrogen 7 from the main condenser is shown which is situated at the top of the low-pressure column 5.

In FIGS. 2 and 3, the dimensions of the cold box are shown, which dimensions determine the transport length TL, the transport height TH and the transport width TB of the package.

In variant exemplary embodiments of the package according to the invention, the cold box, in addition to the double column 3/4/5, can contain one or more of the following apparatuses:

-   -   main heat exchanger     -   subcooling counterflow heat exchanger     -   crude argon column (one-piece or multipiece)     -   pure argon column

A further variant embodiment of the low-pressure column 5 differs from the above described in that the oxygen section E contains an ordered packing made of folded aluminum sheets. The sheets, apart from this coarse folding, have a perforation and a fine fluting. The sheet width thereof is 0.2 mm. The packing has a specific surface area of at least 1000 m²/m³, in particular 1250 m²/m³.

Another variant embodiment differs from the above described in that the argon intermediate section D also contains the special aluminum packing of high specific surface area of the oxygen section E.

In a third and fourth variant embodiment, respectively, instead of the particularly dense aluminum packing of the first and second variants, in each case a copper packing having a sheet thickness of 0.1 mm and a specific surface area of 1200 m²/m³ is used. 

1. A transportable package with a cold box (51), in the interior of which a double column of a low-temperature air separation system is arranged which has a high-pressure column (3) and a low-pressure column (5) which are arranged one above the other, wherein the high-pressure column (3) and the low-pressure column (5) contain mass transfer elements, and the mass transfer elements are formed in at least one subregion (A, B, C, D, E) of the low-pressure column (5) by an ordered packing which is made of folded metal sheets, characterized in that the metal sheets have a sheet thickness of 0.2 mm or less, in that the ordered packing has a specific surface area of at least 1000 m²/m³ and in that at least in a subregion of the high-pressure column (3), the mass transfer elements are formed by rectification plates arranged one above the other which have a plate spacing of less than 195 mm, in particular less than 180 mm.
 2. The package as claimed in claim 1, characterized in that the plate spacing of the distillation plates in the high-pressure column (3) is between 80 and 155 mm, in particular between 95 and 130 mm.
 3. The package as claimed in claim 2, characterized in that the height of the cold box (51) is less than 47 meters.
 4. The package as claimed in claim 1, characterized in that the minimum diameter of the cross section of the cold box (51) is no more than 4.25 meters.
 5. The package as claimed in claim 1, characterized in that the diameter of the cross section of the cold box (51) perpendicular to the minimum diameter is less than 4.95 meters.
 6. The package as claimed in claim 1, characterized in that, in addition, a crude argon column (15) is arranged in the cold box, which crude argon column has a top condenser (19) which is constructed as condenser-evaporator, wherein the evaporation space of the top condenser (19) is connected via a two-phase pipe (21) to the low-pressure column (5), and the two-phase pipe (21) is constructed in such a manner that, in operation of the low-temperature air separation system, not only gas but also liquid flow from the evaporation space of the top condenser into the low-pressure column (5).
 7. The package as claimed in claim 1, characterized in that, at least in a subregion of the low-pressure column in which the metal sheets of the ordered packing which have a sheet thickness of 0.2 mm or less, the metal sheets consist of copper, and in particular have a sheet thickness of 0.1 mm or less.
 8. The package as claimed in claim 1, characterized in that the ordered packing has a specific surface area of greater than 1000 m²/m³, in particular greater than 1150 m²/m³.
 9. The package as claimed in claim 1, characterized in that the low-temperature air separation system is designed for processing more than 10 000 Nm³/h and less than 250 000 Nm³/h of feed air in standard operations.
 10. A method for producing a low-temperature air separation system, in which a cold box (51) is transported to the installation site as a transportable package as claimed in claim 1, the cold box (51) at the installation site is connected to an air compressor for compressing feed air, to a purification unit for compressed feed air, and to a main heat exchanger (2) for cooling purified feed air. 